Floating roller mounting for web tension control systems



May 16, 1961 G. VISCHULIS 2,984,430

FLOATING ROLLER MOUNTING FOR WEB TENSION CONTROL SYSTEMS Filed July 10,1958 2 Sheets-Sheet 1 (0/7 fry/er IINVENTOR.

May 16, 1961 G. VISCHULIS FLOATING ROLLER MOUNTING FOR WEB TENSIONCONTROL SYSTEMS Filed July 10, 1958 2 Sheets-Sheet z United StatesPatent FLOATING ROLLER MOUNTING FOR WEB TENSION CONTROL SYSTEMS GeorgeVischulis, Berkeley, 11]., assignor to Mjehle-Goss- Dexter,Incorporated, Wilmington, Del., a corporation of Delaware Filed July 10,1958, Ser. No. 747,728

Claims. (Cl. 24275.42)

The present invention relates generally to systems for controllingtension in running webs drawn from supply rolls into web processingapparatus. Thus the invention finds special utility in web fed printingpress installations. More particularly, this invention relates to themounting of a floating roller or a tension sensing element in such asystem.

Any web tension control system essentially includes two basiccomponents. One of these is affected by the web tension. The othereffects corrective adjustment upon departure of web tension from apreselected value. The first component can be aptly termed a sensingdevice responsive to web tension changes. The second component, whichusually includes braking means, is related to the first element in thatit is responsive to its operation to maintain a particular web tensionor to produce an increase or decrease thereof. Essentally then, theeffectiveness of the entire system is dependent upon the sensitivity ofthe first element.

Conventionally a floating roller is used as the initial element of thesensing component. This roller is disposed to engage in a horizontalU-shaped loop formed in the web and is suspended for lateral movement inresponse to changes in web tension. Heretofore, in conjunction therewithvarious means such as biasing springs, shock-absorber type devices, orso-called inertia-weights have been employed. Such devices have notproved satisfactory because of their actions in urging the floatingroller into the web loop with varying forces depend ing upon thefloating roller position.

It is a general object of the present invention to provide in a webtension control system a new and improved floating roller mounting whichavoids the disadvantages of prior arrangements and in which provision ismade to compensate for the eflect of gravity without the addition ofsignificant mass and which varies according to the position of thefloating roller regardless of that position.

It is a further object to provide a floating roller mounting which notonly compensates for the eflects of gravity thereon as it is translatedfrom side to side but which also takes into account torque forcesapplied to the floating roller by other elements of the tension controlsystem in which the new and improved mounting is incorporated to the endthat the displacement of the floating roller from a preselected positionis truly representative of web tension variations and so imparts this tothe control system for appropriate corrective action.

It is also an object to achieve the foregoing by comparatively simpleand reliable means which permits of economical manufacture and ofapplication to existing printing press or other web processinginstallations.

Other objects and ancillary advantages are attained by the constructionand arrangement shown by way of illustration in the accompanyingdrawings, in which:

Figure 1 is a diagrammatic representation of a web tensioning system inwhich the features of the present invention are incorporated.

Fig. 2 is an elevational view of a control panel mounting certaincomponents of the system including the novel and improved floatingroller mounting.

Figs. 3 and 4 are fragmentary side elevational views similar to Fig. 2but illustrating relative component relationships in different positionsof the floating roller.

Fig. 5 is a schematic representation of some of the elements of the webtension control system and illustrating the production of turningmoments or torque applied to the floating roller pivot shaft which mustbe compensated for.

Fig. 6 is a graphical representation of the torques according to Fig. 5and of the compensating torque.

While the invention has been illustrated and described in considerabledetail with reference to a particular embodiment, it is to be understoodthat it is not thereby intended that the invention be limited to suchdetail. On the contrary, it is intended to cover all modifications andall the alternative constructions falling within the spirit and scope ofthe invention as defined by the appended claims.

Referring more particularly to the drawings there is diagrammaticallyshown in Fig. l the basic elements of a control system in which theinstant invention is incorporated. The control system as a whole isdisclosed and claimed in applicants co-pending application Serial No.743,728, filed June 23, 1958. Thus it has been only fragmentarilyillustrated in Fig. 1 and as controlling the tension in a paper web Wdrawn from a supply roll 20 into web processing apparatus herefragmentarily indicated as a printing press 21. The supply roll 20 isjournaled for rotation about an axis 20a defined by a shaft extendingbetween a pair of arms 22 of a threearm supply reel. Two other arms areprovided on the reel for carrying replacement rolls. The web is drawn oninto the press 21 by a pair of cylinders 23 comprising a printing couplepowered by a motor M.

In order to apply a braking or a retarding force to the supply roll 20,and thus create tension in the web W, a strap or belt 24 is providedwhich frictionally engages the periphery of the roll 20. The strap isanchored at its opposite ends 24a and 2412. To variably tighten thestrap, it is trained over rollers 25 and 26, the former being stationaryand the latter being carried by the piston of a pneumatic actuator 28.Pressure fluid, in this instance compressed air, is supplied to theactuator so that when the piston of the actuator 28 is moved to the leftthe roller 26 is also urged to the left to tension the strap 24 andincrease the braking force applied to the roll 20 and thereby increasetension in the running web W.

It will be understood by those skilled in the art that several of thestraps 24 and actuators 28 are conventionally associated with a singlesupply roll 20. The straps are spaced apart along the roll and thenumber of straps associated with a particular roll depends upon thewidth of that roll. The actuators 28 are supplied in parallel withcontrolled fluid pressure so as to effect a corresponding braking forceupon the roll.

To sense the tension existing in the running web W, a floating roller 30is utilized. The floating roller is journalled adjacent the lower endsof a pair of arms 31, only one being shown, depending from a pivot shaft32. The web W is trained over stationary guide rolls 34 and 35 so as todefine a substantially horizontal, U-shaped loop in the bight of whichis engaged floating roller 30. The floating roller 30 thus tends to bemoved to the left, i.e., is swung clockwise of the axis of the pivotshaft 32 by the web W with a force or torque which is proportional toweb tension.

The control system includes means which is provided to exert a loadingforce on the floating roller 30 which opposes and counter-balances theforce exerted thereon by the web W. As shown, this means includespressure fluid actuator comprising a loading cylinder 38 having a piston38a slidable therein which is pivotally connected at 39 to a radial arm40 fixed to the floating roller pivot shaft 32. From a suitable source41, pressure fluid is supplied by way of a manually adjustable regulatorvalve 42 to the cylinder 38 so as to cause the piston 38a to exert acounter-clockwise force or torque on the floating roller pivot shaft 32.

The loading actuator, therefore, exerts a reference force or torque onthe floating roller pivot shaft 32. This is a constant force asdetermined by the setting of the regulator 42 regardless of the positionof the floating roller. It thus sets the value or control point ofwebtension which is to be maintained.

It will be appreciated that changes in web tension from a preselectedvalue or control result in lateral movement of the floating roller andthus angular movement of the pivot shaft 32. This angular movement isutilized to control the application of pressure fluid to the brakingactuator 28 to increase or decrease the braking force applied by thestraps 24 to the supply roll 20. For this purpose the illustrativecontrol system includes a pilot controller generally designated 45. Thepilot controller thus forms a control link between the floating roller38 and the braking actuator 28, and it functions to supply pressurefluid from the source 41 to the actuator 28 in proportion to the angulardisplacement of the floating roller 30 from a preselected referenceposition. The pilot controller is equipped with a control rod 49 andinterposed between it an arm 50 fixed to the pivot shaft 32 is a spring52 imparting a force to the rod that is proportional to the movement ofthe roller 30 for effecting movement of a valve mechanism within thecontroller to control presure fluid output from the controller. In otherwords, as the floating roller 30 and its support arms 31 are swung froma reference position, the spring 52 is compressed an amountcorresponding to the angular displacement thereof and by virtue of thespring 52, the movement of the valve mechanism Within the pilotcontroller 45 can be extremely limited. Thus the spring 52 remains incompression even though the floating roller pivot shaft 32 is angularlydisplaced through a considerable arc.

From the foregoing then it will be seen that the pilot controller spring52 exerts an upward force continuous- 1y, which force acting through thearm results in a clockwise torque upon the floating roller pivot shaft32.

To impart stability to the system, damping means is provided which, too,is associated with the floating roller 30. For illustrative purposesthis damping means has been shown as a double acting dashpot 54 having afluid filled cylinder 54a in which a ported piston 54!) is slidable. Thepiston 54b is equipped with a rod which is pivotally connected to anddepends from an arm 56 extendng radially from the pivot shaft 32. Theweight of the piston 54b acting through the arm 56 also results in theapplication of a torque to the pivot shaft 32.

As hereinbefore noted, the floating roller 30 is journalled at the lowerends of supporting arms 31 which are fixed to the pivot shaft and dependtherefrom. Conventionally floating rollers possess considerable weight.When the floating roller 30 is positioned directly beneath the pivotshaft, i.e., its axis and that of the pivot shaft 32 are in the samevertical plane, the force of gravity acting thereon results in theapplication of no torque to the pivot shaft. But when the floatingroller is displaced from such position, the force of gravity causes atorque to be applied to the pivot shaft 32 which varies according to thesine of the angle of displacement. This torque is counter-clockwise indirection when the floating roller is moved to the left and is clockwisein direction when the floating roller is moved to the right of avertical plane passing through the pivot shaft axis.

To summarize then, the pilot controller spring 52 applies a torque in aclockwise direction to the pivot shaft 32 which varies according to theamount of compression applied to the spring which in turn corresponds tothe angular displacement of the pivot shaft. There is also a clockwisetorque applied to the pivot shaft as a result of the weight of thepiston 54b of the damping dashpot 54. Yet another torque is applied tothe pivot shaft 32 which may be either clockwise or counterclockwisewhich torque results from the force of gravity acting on the floatingroller when it is displaced from a vertical position beneath the pivotshaft. The resultant net torque on the pivot shaft as thus set forthcould adversely affect the functioning of the floating roller as asensing device.

In accordance with the present invention there is provided an improvedfloating roller mounting in which provision is made to compensate forthe torque resulting from the effect of gravity upon the floating rollerand which also compensates for the torques applied by the pilotcontroller spring 52 acting through its lever arm and the weight of thedamping dashpot piston acting through its lever arm. As a result theangular displacement of the floating roller from a position, whichrepresents the preselected tension for a given set of operatingconditions including roll diameter and changing press speed, whateverthat position might be, is truly representative of tension variation inthe running web W. Thus there is imparted to the control systemincorporating this novel mounting a signal unaffected by theaforementioned torque forces to the end that appropriate correctiveaction can be effected to restore web tension to the preselected value.

In carrying out the invention the improved floating roller mountingutilizes a cam mechanism, generally designated 58, which includes a cambiased into engagement with a cam follower roller which is carried by anarm that is rigid with the pivot shaft. In general terms, this mechanismis constructed and arranged to exert a torque on the pivot shaft whichcompensates for the resutlant net torque created as hereinbeforedescribed.

Referring more particularly to Fig. 2 of the drawings, there shown is afloating roller mounting embodying the features of the present inventionas derived from one particular commercial installation. Thisillustrative embodiment includes a control mounting panel 60 which isadapted to be fixed to the web processing apparatus, e.g., the frame ofthe printing press 21. Extending through the panel 60 is one end of thefloating roller pivot shaft 32. Behind the panel and fixed to the shaft32 is one of the floating roller suport anms 31 in the lower end ofwhich is journalled the floating roller 30. Forwardly of the panel andfixed to the pivot shaft 32 is a hub 62. The lever arms 40, 5G and 56,respectively, which were diagrammatically indicated in Fig. 1, arepreferably formed integral with and project radially outward from thehub 62. Both the loading cylinder 38 and the damping dashpot 54 aremounted upon the control panel and provision is made to accommodatechange of pivot location due to angular displacement of the floatingroller pivot shaft 32 and thus of the arms 40, 5t and 56. For example,as indicated at 64 the damping dashpot cylinder 54a is pivotallyattached at its lower end to a mounting bracket 65 which is attached tothe panel 6%). The pilot controller 45 is fixed to the panel 60 by meansof a suitable bracket 66.

As shown, the control rod 49 of the pilot controller 45 extends upwardlyfrom the pilot controllers housing. The pilot controller spring 52 isinterposed between the upper end of the control rod 49 and the hub arm59 and a self-aligning coupling 67 is provided between the lower end ofthe spring 52 and the control rod 49. In order to maintain the spring inposition, a guide rod 68 is provided which is seated in the coupling 67'and extends freely through a collar 69 pivoted on a pin 70 adjacent theouter end of the arm 50. The upper end of the controller spring 52engages the collar 69. Thus, as the hub 62 is angularly displaced withthe shaft 32, according to the displacement of the floating roller 30,the arm 50 moves the collar along the rod and increases or decreases thecompression of the pilot controller spring to increase or decrease theforce exerted thereby upon the control rod of the pilot controller.

The cam mechanism 58 includes a cam 72 having a cam face 72a which isbiased into engagement with a cam follower roller 74 by a preloadedspring 75. The cam follower roller 74 is mounted on the pivot pin 70disposed adjacent the outer end of the arm 50. Centrally of the outerside thereof the cam 72 is equipped with a self-aligning coupling 76against which one end of the spring 75 bears and which receives one endof a spring-positioning rod 78. The other end of the rod 78 is slidablyreceived in a self-aligning coupling 79, and against which the other endof the spring 75 bears. The latter coupling is mounted in a hollowcompression adjustment nut 80 which in turn is screw-threaded into ananchor block 81 that is fixed to the panel 60.

The cam mechanism 58 is so oriented that when the floating roller pivotshaft 32 is disposed in a neutral position, i.e., when the algebraic sumof all the torques, or net torque, applied to the pivot shaft is Zero,the force exerted by the cam mechanism upon the cam follower 74 actsalong a line that passes substantially through the axis of the pivotshaft 32 so as to impart no torque thereto. Torque forces acting aboutthe pivot shaft 32 are represented schematically in Fig. 5. A review ofthis figure will show that zero net torque results when the floatingroller is displaced slightly to the left. The displacement will be suchthat the torque thus created will be equal in magnitude and opposite insense to torque applied by the controller spring 52 and the dashpotpiston 5412 as mentioned above. As a result, when the pivot shaft is ina neutral position the arms 40 and 50 and 56 of the hub 62 arecorrespondingly displaced. In the illustrative embodiment when the cammechanism is oriented so that the line of action of the force exertedthereby passes through the center line of the cam follower 74 and theaxis of the shaft 32, the mechanism is angularly offset approximatelyseven degrees from horizontal.

It will be appreciated that as the web W is withdrawn from the supplyroll and is consumed by web processing apparatus such as theillustrative printing press 21, the diameter of the supply roll 20decreases. As it decreases, gradually, the angle of wrap of the straps24 decreases, and thus the braking actuator 28 must exert anincreasingly greater force upon the straps so as to maintain the sametension in the web as determined by the preselected reference forceexerted on the floating roller 30 by the loading actuator 38. Desirably,therefore, the floating roller 30 is initially displaced to the left andgradually moves in a counter-clockwise are so as to increase thedownward force on the control rod 49 of the pilot controller 45 throughthe pilot controller spring 52 whereby to control the pressure fluidoutput from the pilot controller 45 to the braking actuator 28. It willbe appa ent, then, that when the floating roller is displaced to theleft of a vertical plane passing through the pivot shaft axis that theforce of gravity acting on the floating roller 30 produces acounter-clockwise torque upon the pivot shaft 32, and to compensatetherefor the cam mechanism 58 must exert a force on the cam followerroller 74 along a line of action that results in a compensating orcounter-balancing, clockwise torque. Similarly, when the floating rollerhas its axis displaced to the right of the pivot shaft axis, the forceof gravity on the floating roller results in the production of aclockwise torque. To counterbalance this force the line of action of thecam mechanism 58 acting upon the cam follower roller 74 must be solocated as to produce a compensating counter-clockwise torque.

To this end two pivots 82 and 83 are provided for the cam 72. The pivotsare spaced equidistant-1y on opposite sides of the center line of themechanism for engagement by notches 72b and 72c formed on the side opposite the sam surface 72a and adjacent the ends of the cam 72.Referring to Fig. 3 of the drawings it will be seen that when thefloating roller 30 is displaced to the left of the axis of the pivotshaft 32, the cam follower 74 engages the sam surface 72a between thecenter line of the mechanism 58, along which line the force of thespring 75 is applied to the cam 72, and the pin 82. Thus the cam pivotsupon the pin 82, and the spring 75 applies clockwise torque to the pivotshaft 32 through the cam 72 and cam follower 74. Alternatively, when thefloating roller 30 is displaced to the right of the pivot shaft axisengagement of the cam follower 74 with the cam surface 72a occursbetween the center line of the mechanism 58 and the pin 83. In thiscondition, as shown in Fig. 4, the cam 72 fulcrums upon the pin 83, andcounterclockwise torque is applied to the pivot shaft 32.

From the foregoing it will be seen that the greater the angle ofdisplacement of the floating roller 30 within its operation limits, thegreater will be the distance between the center line of the mechanismand the point of engagement of the cam follower with the cam surface72a. This results in a corespondingly increased effective lever by whichthe compensating force of the spring 75 is applied to the pivot shaft32. Thus as the displacement of the floating roller increases the forceapplied to the cam follower is directed along a line of action asdetermined by the cam surface to effect the required counterbalancing orcompensating torque.

It can be appreciated that the compensating torque exerted by the cammechanism 58 on the pivot shaft 32 depends both on the force exerted bythe spring 75 and the position, relative to the shaft 32, of the line offorce exerted by the cam 72 against the roller 74. In the illustratedembodiment, the force of the spring 75 is controlled by the adjustmentnut The position of the line of force exerted by the cam 72 relative tothe shaft 32 is desirably determined by the shape of the cam 72 sincethe cam force acts perpendicularly of the cam face 72a. In the preferredconstruction, the cam face 72a is slightly concave so that the propermoment arms are obtained, considering the strength of the spring 75 andthe weight of the floating roller 30, to exert the proper balancing orcam torque on the shaft 32 in all angular positions assumed by theshaft.

In order to graphically illustrate the foregoing Figs. 5 and 6 have beenincluded in the drawings. Fig. 5 schematically represents theapplication of torques to the axis of the pivot shaft 32 with a range oflateral or angular displacement of the floating roller 30 through anoverall angle of some 50, 25 on each side of a vertical plane passingthrough the pivot shaft axis. The resulting torques are plotted in Fig.6. Therein the torque due to the weight of the damping dashpot piston54b is represented by the line T It will be noted that this is asubstantially constant torque in a clockwise direction. In theillustrative device no force is exerted upon the hub 62 by thecontroller spring 52 when the floating roller 30 is in the limitposition to the left of the pivot axis. This condition exists from thelimit position until the floating roller moves clockwise through an arcof approximately five degrees. Thereafter it will be seen that thistorque increases in a clockwise direction as the controller spring 52 iscompressed by displacement of the floating roller axis to the right.This is indicated by the line T The torque due to the effect of gravityaccording to the floating roller position is indicated by the line T Itwill be seen that at zero degrees, as indicated in Fig. 6, this torqueis maximum in a counter-clockwise direction. It decreases to zero at the25 point, when the floating roller axis occupies the vertical plane thatpasses through the pivot shaft axis, and then increases in a clockwisedirection as the floating roller moves toward the 50 position indicatedin Fig. 6. These three torques as represented by the lines T and T and Tcan be added graphically. The result of such addition is represented inFig. 6 by the line T This is the resultant net torque upon the pivotshaft axis and represents the torque which is compensated for by the cammechanism 58 that comprises a part of the instant floating rollermounting. Thus to compensate therefor the doublepivoted, spring-biasedcam 72 effects a compensating torque equal in magnitude but opposite insense to the resultant net torque line T and is represented by the lineT From the foregoing it will also be seen that the preloaded spring 75applies a substantially constant biasing force to the cam 72 because theconstruction and arrangement as described limits the range of physicalmovement of the spring. A particularly practical advantage of theforegoing construction and arrangement is that the novel floating rollermounting permits of adjustment by the single operation of positioningthe adjustment nut 80 within the anchor block 81 whereby to determinethe amount of preloading of the spring 75.

From the foregoing, therefore, it will be seen that the improvedfloating roller mounting not only compensates for the efiects of gravityresulting from angular displacement of the floating roller, but it alsotakes into account torque forces applied by other elements of thetension control system of which the mounting is a part. As a result thedisplacement of the floating roller from a position representing apreselected tension is truly representative of variations in web tensionand so imparts an accurate signal to the control system for appropriatecorrective action. It will also be apparent that the foregoing isachieved by comparatively simple and reliable means which permits ofeconomical manufacture and of application to existing printing press orother web processing installations. More particularly in this latterregard it avoids the necessity for changing the loading automatically tocompensate for the torques mentioned previously which would be a complexand expensive undertaking. Additionally, the floating roller mountingconstructed in accordance with the teachings of the present inventioneffects compensation in both directions of angular displacement of thefloating roller with respect to the pivot shaft, yet it requires but asingle preloaded biasing spring. Of especial importance is the fact thatthis mounting adds no significant mass to the floating roller system.

I claim as my invention:

1. In a web tension control system having a frame for carrying afloating roller which engages a loop in the web, a floating rollermounting comprising, in combination, a pivot shaft journaled in saidframe, a support arm fixed to said pivot shaft for journaling thefloating roller in a preselected position which is in substantiallyvertical depending spaced relation beneath said pivot shaft, a secondarm fixed to said pivot shaft and extending radially therefrom inangularly spaced relation to said support arm, and a compensatingmechanism including a spring biased cam anchored to said frame andengageable with said second arm for applying a torque to the pivot shaftequal in magnitude and opposite in direction to the torque appliedthereto due to gravity as a result of displacement of the floatingroller from said preselected position beneath said pivot shaft.

2. In a web tension control system having a floating roller for engaginga loop in the web, a floating roller mounting comprising, incombination, a pivot shaft, a support arm fixed to said pivot shaft forjournaling the floating roller in depending spaced relation to saidpivot shaft, a second arm fixed to said pivot shaft and disposed inangularly spaced relation to said first arm, and a compensatingmechanism including a cam engageable with said second arm, a biasingspring engageable with said cam centrally thereof for applying a forceby way of said cam to said second arm along a line of actionsubstantially through the pivot shaft axis when the same is in neutralposition, a pair of fulcrum pins disposed in spaced relation to eachother and on opposite sides of the aforesaid line of action foralternative fulcruming engagement therewith by the respective ends ofsaid cam on the opposite side thereof from said second arm for applyinga compensating force along lines of action on either side of and spacedfrom the aforesaid line of action according to the angular displacementof the shaft axis as the position of the floating roller changes so asto counteract the torque applied to the pivot shaft as a result ofdisplacement of the floating roller from neutral position as it changesduring operation of the system.

3. In a web tension control system having a floating roller for engaginga loop in the web and having a pressure fluid operated system forregulating tension in the web including a pressure fluid operatedloading device and a pressure fluid supply controller having a springbiased control rod, a floating roller mounting comprising, incombination, a pivot shaft adapted for connection with the loadingdevice, a support arm fixed to said pivot shaft for journaling thefloating roller in spaced relation to said pivot shaft, a second armfixed to said pivot shaft in angularly spaced relation to said supportarm and having the force of the controller biasing spring exertedthereon, and a compensating mechanism including a cam and a preloadedspring biasing said cam into engagement with said second arm forapplying a torque to said pivot shaft equal in magnitude and opposite indirection to the resultant net torque applied thereto as a result of theaction of the controller biasing spring and of gravity according to theangular position of the floating roller with respect to the axis of saidpivot shaft.

4. In a web tension control system having a floating roller for engaginga loop in the web and having a pressure fluid operated system forregulating tension in the web including a pressure fluid operatedloading device and a pressure fluid supply controller having a springbiased control rod, a floating roller mounting comprising, incombination, a pivot shaft adapted for connection with the loadingdevice, a support arm fixed to said pivot shaft for journaling thefloating roller in spaced relation to said pivot shaft, a second armfixed to said pivot shaft in angularly spaced relation to said supportarm and having the force of the controller biasing spring exertedthereon, and a compensating mechanism including a cam and a preloadedspring biasing said cam into engagement with said second arm forapplying a force to said second arm along a line of action substantiallythrough the axis of said pivot shaft when the same is in neutralposition, a pair of fulcrum pins disposed in spaced relation on oppositesides of the aforesaid line of action for alternative fulcrumingengagement by said cam for applying a compensating force to said secondarm along lines of action on either side of the aforesaid line of actionaccording to the angular displacement of said pivot shaft axis as theposition of the floating roller is changed so as to compensate for theresultant net torque applied to the pivot shaft by the force of thecontroller spring and the force of gravity according to the angularposition of the floating roller with respect to said pivot shaft.

5. In a system for regulating tension in a moving web by means of africtional retarding force applied to the periphery of a web supply rollby stationary belts, the combination comprising a floating rollerswingably supported on an axis and adapted to engage in a loop in themoving web, means for applying a preselected force to the floatingroller and hence to the web for positioning said roller, and acontroller responsive to displacement of the floating roller, said meanssaid; floating roller and said controller being interconnected at saidsupport axis amount according to the displacement of the floating of thefloating r ll d a mechanism f t roller by operational variations in webtension. balancing torque variations due to floating roller displace-References Cited in the file of this patent ment during operation of thesystem, said mechanism 1ncluding two spaced pins and a spring biased campivot- 5 UNITED STATES PATENTS able selectively on either of said pinsfor applying com- 2,334,164 Lotz Nov. 16, 1943 pensating torque aboutthe support axis in direction and 2,733,876 Laycock Feb. 7. 1956

